Drupal's hook system allows for modules to interact and alter the workings of other modules or even Drupal core itself. It is a very simple system that allows modules to even create their own very easily. In common practice, there are two types of hooks that you would want to create - alter hooks and intercepting hooks. Alter hooks provide a common way to edit the contents of a particular object or variable, typically using drupal_alter(). Intercepting hooks allow external modules to perform actions during the execution of another module.
Example #1 (simple invoking)
<?php
// will call all modules implementing hook_hook_name
module_invoke_all('hook_name');
?>Example #2 (aggregate results)
<?php
$result = array();
foreach (module_implements('hook_name') as $module) {
// will call all modules implementing hook_hook_name and
// push the results onto the $result array
$result[] = module_invoke($module, 'hook_name');
}
?>Example #3 (altering data using drupal_alter)
<?php
$data = array(
'key1' => 'value1',
'key2' => 'value2',
);
// will call all modules implementing hook_my_data_alter
drupal_alter('my_data', $data);
?>Example #4 (passing by reference cannot use module_invoke)
<?php
// @see user_module_invoke()
foreach (module_implements('hook_name') as $module) {
$function = $module . '_hook_name';
// will call all modules implementing hook_hook_name
// and can pass each argument as reference determined
// by the function declaration
$function($arg1, $arg2);
}
?>
Comments
another tip
Submitted by unterwassergehäuse on
i got a little bit stuck when trying to implement a drupal_alter. so a tip for others reading this.
my hook: drupal_alter('graphapi_build_graph_data', $graph, $vars);
ist verry important that if you call it later you add & to the parameter you want to alter
function MYMODULE_graphapi_build_graph_data_alter(&$graph, $vars) ....
cheers
marco
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